The instant invention relates to an acceleration-responsive system and method for triggering vehicle safety devices such as air bags that operate to protect vehicle passengers in the event of a crash or sudden vehicle deceleration.
The prior art teaches a variety of systems and methods for sensing a vehicle crash or sudden vehicle deceleration and deploying a vehicle safety device such as an air bag, or locking a seat belt, or actuating a pretensioner for a seat belt retractor. Typically, the safety device is triggered or otherwise deployed into its protective position when the system detects an impact or deceleration exceeding a threshold value therefor. One such "physically-based" prior art method of crash detection using an electronic acceleration sensor integrates the output thereof over time and compares the result against a threshold velocity. One problem with the integration method of crash detection is that the crash severity cannot be determined early enough for high-speed angular, partial barrier, or pole crashes. Moreover, the wide "grey area" between "fire" and "no-fire" conditions for low-speed crash conditions often results in an inadvertent deployment of the safety device when deployment is unnecessary, or a non-deployment of the safety device when deployment is necessary. Additionally, the safety device often will not be activated during low speed crashes and will not be activated instantaneously or quickly enough to prevent injury during high speed frontal crashes or for pole or offset crashes.
A second known method of crash detection using an electronic sensor attempts to deemphasize the use of simple velocity calculations and instead measure the energy dissipated during a crash to assess the crash. However, this "energy method" still utilizes velocity information, resulting in the same types of deployment problems and slow response time encountered with the integration method. Additionally, the energy method has a further limitation of detection capability in that it is accurate only over short time intervals.
Another known method of crash detection uses in combination a jerk algorithm indicative of rate of change of vehicle deceleration with a second algorithm indicative of vehicle deceleration itself. A unanimous vote under both algorithms is required to trigger the safety device. Unfortunately, the requirement of unanimity of decision can prevent activation of the safety device if the vehicle crash involves the collision of a vehicle against the side structure of another vehicle.